The invention is directed to a process and a system for the solution mining of evaporites and preparation of the obtained saline solution, in particular for the dissolution of salts, evaporation and cooling of the obtained saline solution, and crystallization of salts under subtropical and tropical climatic conditions. The invention can also be used for the preparation of naturally occurring saline solutions.
The amount of energy required for evaporating water out of a saline solution corresponds to the evaporation heat of water from the respective saline solution. Two techniques are known from the prior art to accomplish this. In the first technique, the saline solution is heated to boiling. The solution boiling point can be lowered by applying a vacuum. This type of water evaporation is carried out in specially constructed evaporating installations. Primary energy use can be reduced to a reasonable level through the utilization of waste heat and secondary energy. In addition to concentrating the saline solution, the use of evaporating installations is also suitable for obtaining and recovering the water as a condensate.
Solar evaporation is used only for concentrating saline solutions. In solar evaporation systems, water is evaporated out of a saline solution which is introduced in large evaporation pools. This evaporation is performed at a very low air humidity at the ambient or surrounding temperature and atmospheric pressure. The evaporated water escapes to the atmosphere and, in contrast to the first-mentioned technique, can not be recovered.
Obviously, solar evaporation is only possible or economically feasible under determined climatic conditions. However, under favorable climatic conditions such as those in the Dead Sea, solar evaporation of saline solutions is economically superior to water evaporation in evaporation plants.
A high-intensity solar radiation similar to that in the Dead Sea region is found in numerous subtropical and tropical regions. However, the air humidity is usually too high for effective water evaporation or the amount of precipitation largely compensates for the quantity of water evaporated. Also, when taking advantage of seasonal dry periods, the required dimensions of the evaporation pools are so large as to render an economical solar evaporation impossible.
Consequently, in these cases evaporation plants are resorted to even though these plants often are not as energy favorable as in temperate regions because of high outside temperatures.
Examples of applications which demonstrate the great variety of the prior art described above are found in the fields of NaCl--boiled salt production, potash fertilizer production, and seawater desalination.
Likewise, it is generally known that water evaporation is also carried out when heated cooling water or condensing water is cooled in cooling towers. Naturally, this water evaporation effect also occurs in the much less commonly practiced cooling of saline solutions in cooling towers (DD 139 354 and DD 155 316).
Also, it is generally known that solar cells are increasingly being used for heating consumer water. For greater heat energy requirements, it is known from the prior art to apply the principle of solar cells to a so-called solar pond, i.e., a pool filled with liquids of different densities which converts the incident solar radiation into heat energy. Typical examples describing the prior art with respect to solar ponds are found in DE 34 22 481, G 85 27 665.0, and the publication "Salt Ponds: Energy Phenomenon" (Compressed Air Magazine, January 1986).
The dissolution of salt deposits by means of solution mining is generally known and the solution mining of NaCl using water as the solvent is very common. Selective solution mining of potassium deposits with the use of a heated solvent is described in the following prior art references: DD 206179, DD 208389, DD 271731, DD 271732, DD 277718, DD 291601, and the publication "Operation of a potassium ore pilot cavern", Colome and Rose, SMRI meeting, October 1994, Hannover.
Thus, it is an object of the present invention to provide a process and a system for the solution mining of evaporites and preparation of saline solutions, which process and system can be used under subtropical and tropical climatic conditions while avoiding the disadvantages resulting from high air humidity and considerable amounts of precipitation.